1. Field of the Invention
The present invention relates to the field of treatment of blood through extracorporeal circulation. More particularly, the invention concerns the treatment of blood where a certain quantity of liquid is extracted and is compensated for at least in part by the reinjection of a substitute liquid, as is done, for example with haemofiltration or haemodiafiltration.
2. Description of the Related Art
It is known to use a balance system to control equality between a quantity of liquid withdrawn from a patient and a quantity that is injected. For this purpose, the drawn-off liquid is collected in a bag, while the injected substitute liquid is taken from a bag. Each of the bags is hooked onto a balance. The reinjection flow rate of the substitute liquid is then controlled in accordance with the data supplied by the balance. Such a system, although reliable, has the disadvantage of being part of equipment that is expensive and difficult to operate.
If liquid withdrawn from a patient is set using a pump and the injection of a substitute liquid is also controlled by a pump, it is known that the balance between the quantity drawn off and the quantity of liquid injected can be controlled by setting the delivery rates of the pumps. This control, based on a flow meter, has the advantage of being simpler to operate and less expensive than control by weight analysis. However, a drawback with this system is that it is not completely reliable since a discrepancy may exist between the apparent delivery provided by a pump and its actual delivery.